1. Field of the Invention
The present invention relates to a metal film pattern and a manufacturing method thereof. A wiring substrate having the metal film pattern of the present invention formed thereon is utilized in various applications such as flat panel displays (e.g., liquid crystal display devices (LCDs), plasma display devices (PDPs), electrochromic display devices (ECDs) and electroluminescent display devices (ELDs)), two-dimensional image detectors, and various electric circuit boards. The metal film pattern of the present invention can also be used as a photomask.
2. Description of the Background Art
In flat panel displays including liquid crystal display devices (LCDs), a display material such as a liquid crystal material or discharge gas is interposed between a pair of substrates. The display material is driven by applying a voltage thereto. Electric wirings of a conductive material are formed on at least one of the substrates.
For example, in the active-matrix display, gate electrodes and data electrodes are arranged in a matrix on one of a pair of substrates having a display material interposed therebetween (i.e., an active matrix substrate). A thin film transistor (TFT) and a picture element electrode are provided at every intersection of the gate electrodes and the data electrodes. The gate electrodes and the data electrodes are normally formed from a metal material such as Ta, Al or Mo by using a vacuum film-formation method such as sputtering method.
The size of a mother substrate used in a manufacturing process of such a flat panel display is ever increasing, and formation of metal wirings (electric wirings) on a large-area substrate on the order of meters is increasingly demanded. However, forming metal wirings on such a large-area substrate by a conventional vacuum film-formation method is problematic in the following points: it is difficult to form metal films having a uniform thickness and quality; and a huge vapor film-formation apparatus and thus an enormous amount of investment in plant and equipment are required.
Moreover, a vapor film-formation apparatus such as a sputtering apparatus and CVD (Chemical Vapor Deposition) apparatus requires a large amount of electric power such as that for driving a vacuum pump, heating a substrate and generating plasma. Of course, energy consumption of the manufacturing apparatus is also increased with increase in size thereof.
Moreover, a metal wiring pattern must be formed by forming a metal film over the whole surface of a substrate by using a vapor film-formation apparatus and then etching away the most part of the metal film (i.e., unnecessary part of the metal film). This causes waste of the metal material (i.e., low material utilization rate). In particular, reduction in energy consumption in the manufacturing process and suppression of the waste of material resources (effective utilization of material resources) are recently strongly demanded due to environmental concerns.
One way to solve the above problems caused by the vacuum film-formation process is to form metal wirings by using a wet film-formation technology instead of a vacuum film-formation method. For example, Japanese Laid-Open Publication No. 4-232922 discloses a method for forming a metal film of Cu, Ni or the like on an underlying film by using a plating technology. In this method, a transparent electrode of ITO (Indium Tin Oxide) or the like is used as the underlying film. This method does not use a vacuum film-formation apparatus to form the metal film. This suppresses increase in investment for manufacturing facility and increase in energy consumption in the manufacturing process. Moreover, the metal film can be selectively formed only on the ITO film by a plating method. This suppresses the waste of the metal material.
In this case, the metal film is formed by the plating technology that does not use a vacuum film-formation apparatus. However, the ITO film serving as an underlying film for the metal film is still formed by a dry vacuum film-formation technology such as a sputtering method and vapor deposition method. Accordingly, the above problems involved in the vacuum film-formation process cannot completely be solved.
Japanese Laid-Open Publication No. 2001-032086 discloses a method for forming even an underlying oxide film (e.g., ITO film), i.e., an underlying film for the metal film, by using a wet film-formation technology. In other words, this publication discloses a method for forming both an oxide film serving as an underlying pattern and various metal films selectively formed thereon by a wet film-formation process. In this method, the underlying pattern (oxide film) is formed by using a sol-gel method, one of the wet film-formation technologies, and a metal film (e.g., a laminated film of Ni, Au and Cu) is selectively formed only on the oxide film by using a wet plating method.
The sol-gel method is a method for producing an oxide solid by producing a sol-gel solution by using an organic or inorganic compound of a metal and a solvent, applying the sol-gel solution to a substrate, promoting hydrolysis and polycondensation reaction of the compound on the substrate so as to solidify a sol into a gel, and heating the gel. The use of the sol-gel method enables the oxide film to be formed by merely applying a sol-gel solution to a substrate such as glass and baking the resultant substrate. This eliminates the need to use a vacuum film-formation apparatus as in the conventional example.
The use of a method in which a sol-gel solution is blended with a photosensitive (photopolymerizable or photodegradable) material in advance or a method utilizing a photolysis reaction of a gel film chemically modified with a chelating agent enables patterning of a sol-gel applied film by a photolithography technology. By optimizing the composition of a sol-gel solution and the conditions for application and baking processes facilitates formation of a thin oxide film having a thickness of 0.1 xcexcm or less and even a fine pattern having a line and space (L/S) of 10 xcexcm or less. Therefore, an oxide film formed by the sol-gel method is optimal as an underlying film for a metal wiring pattern.
Note that, in the specification, the following method for forming an oxide film also falls within the category of the sol-gel method in a broad sense: in order to improve the stability of a sol in the atmosphere, a metal chelate complex solution with its hydrolysis and polycondensation reaction suppressed is used as a solution to be applied to the substrate, and an oxide film is formed by thermal decomposition of the metal chelate complex film.
The inventors formed metal wirings by an electroless nickel (Ni) plating method on an oxide film formed by a sol-gel method. In this experimentation, the inventors found that the metal film is deposited outside the pattern depending on the composition of the electroless nickel plating solution and such deposition outside the pattern is remarkable in a fine line pattern portion, and particularly in a portion having a line-space of 10 xcexcm or less. When such deposition outside the pattern occurs in fine wirings, the insulating property between patterns is degraded, and in a worse case, short-circuiting occurs. Accordingly, deposition outside the pattern must be eliminated as much as possible upon forming the metal wirings.
It is an object of the present invention to prevent deposition of a metal film outside the pattern from occurring in a fine line pattern portion, and particularly in a portion having a line-space of 10 xcexcm or less, when a metal film pattern is formed by an electroless plating method.
According to one aspect of the present invention, a method for manufacturing a metal film pattern includes the steps of: forming an oxide film having a prescribed pattern feature on a substrate by a wet film-formation technology; and forming a metal film on the oxide film by an electroless plating method. The electroless plating method is conducted in the presence of at least one sulfur-containing compound selected from the group consisting of thiosulfates, thiocyanates and sulfur-containing organic compounds. According to the present invention, deposition outside the pattern is prevented even when the oxide film pattern formed by, e.g., a sol-gel method is a fine pattern having a line and space (L/S) of 10 xcexcm or less. As a result, a metal film can be formed on the oxide film in an excellent manner.
In the manufacturing method of the present invention, the sulfur-containing compound preferably has a concentration of 0.001 mg/L to 20 mg/L. Since the sulfur-containing compound is present at 0.001 mg/L or more in an electroless plating solution, deposition outside the pattern can be effectively suppressed in the electroless plating process. Moreover, since the sulfur-containing compound is present at 20 mg/L or less in the electroless plating solution, the oxide film pattern can be reliably plated with the metal film without causing significant reduction in metal deposition rate and stopping of the plating.
In the manufacturing method of the present invention, the oxide film is preferably formed using a photosensitive sol-gel solution. The method preferably further includes the step of patterning the oxide film with a prescribed feature by a photolithography technology. This enables a fine pattern having a line and space (L/S) of 10 xcexcm or less to be formed by a simple process.
According to another aspect of the present invention, a metal film pattern having a prescribed feature has a laminated structure of an oxide film formed by a wet film-formation technology and a sulfur-containing metal film formed thereon.
In the metal film pattern of the present invention, deposition outside the pattern is prevented even when the oxide film pattern formed by, e.g., a sol-gel method is a fine pattern having a line and space (L/S) of 10 xcexcm or less. As a result, a metal film is formed on the oxide film in an excellent manner. This prevents short-circuiting caused by deposition outside the pattern. Moreover, the metal film pattern of the present invention can be manufactured without using a vacuum film-formation apparatus. This enables increase in investment in manufacturing facility relating to film formation and increase in energy consumption in the manufacturing process to be suppressed even when a large-area substrate is used. Since the metal film pattern of the present invention need not have vacuum-resistant and heat-resistant properties, an insulating substrate of an organic material (e.g., polymer film) can be used in addition to a glass substrate. This enables the metal film pattern of the present invention to be efficiently manufactured by using a very long film base material and a roll-to-roll method. The metal film pattern of the present invention can be selectively formed by a plating method on the oxide film formed by a wet film-formation technology (e.g., sol-gel method). This suppresses waste of a metal material. Accordingly, a wiring substrate that can be used in various applications such as flat panel displays, two-dimensional image detectors and various electric circuit boards can be provided inexpensively.
According to still another aspect of the present invention, a display device uses a wiring substrate having the metal film pattern of the present invention formed thereon. Accordingly, short-circuiting caused by deposition outside the pattern is prevented. Moreover, a display device capable of being manufactured at low costs and applicable to a large-area substrate can be provided.
According to yet another aspect of the present invention, an electroless plating solution for forming a metal film on an oxide film formed by a wet film-formation technology contains at least one sulfur-containing compound selected from the group consisting of thiosulfates, thiocyanates and sulfur-containing organic compounds. The electroless plating solution of the present invention is suitable for manufacturing of the metal film pattern of the present invention.